DESCRIPTION (PROVIDED BY APPLICANT: The goal of this project is to determine whether pharmacologic induction of Mrp3 can be used as a means of hepatoprotection in humans during cholestatic disease states. Mrp3, which is normally expressed at low levels, serves to export a wide range of organic anions from the liver, back to the blood, thereby decreasing their exposure and toxicity to the liver. Mrp3 expression is significantly increased both in response to certain microsomal enzyme inducers as well as during cholestasis in rodents. Human expression of Mrp3 is also increased in certain liver diseases. Mrp3 expression can be pharmacologically increased by certain microsomal enzyme inducers in both mouse and rat. However, the mechanism for the induction of Mrp3 appears to be a complex interaction where transcriptional studies performed in vitro are unable to accurately replicate the induction observed in vivo. Aims 1 and 2 are designed to determine whether human Mrp3 expression can be pharmacologically induced by this same mechanism. These are;1. Determine the common mechanism for the cholestatic and pharmacologic induction of Mrp3 expression. 2. Determine whether the human Mrp3 gene can be induced in vivo using a unique transcriptional activation assay and human liver slices. Cholestasis is a very complex disease with multiple etiologies that results in the accumulation of bile acids and other organic anions that cause profound hepatocellular damage. If Mrp3 can be pharmacologically induced in humans as a means of eliminating hepatic exposure to the toxic effects of accumulating bile acids and other organic anions, this would represent an important means of hepatoprotection during cholestasis. Aims 3 and 4 have been designed to determine whether Mrp3 induction can be used as a legitimate drug target in the treatment of human liver disease. These are;3. Determine whether microsomal enzyme inducers that increase expression of Mrp3 are capable of altering the disposition of biliary constituents and protecting against hepatotoxicity during cholestasis. 4. Determine whether the transgenic overexpression of human Mrp3 is hepatoprotective in models of cholestasis.